avsa242/max31856-spin

P8X32A/Propeller, P2X8C4M64P/Propeller2 driver object for the Maxim max31856 thermocouple amplifier

max31856-spin

---

This is a P8X32A/Propeller, P2X8C4M64P/Propeller 2 driver object for Maxim's MAX31856 SPI Thermocouple amplifier IC.

IMPORTANT: This software is meant to be used with the spin-standard-library (P8X32A) or p2-spin-standard-library (P2X8C4M64P). Please install the applicable library first before attempting to use this code, otherwise you will be missing several files required to build the project.

Salient Features

• 4-wire SPI connection at up to 1MHz (P1), 5MHz (P2)
• Reads on-chip cold-junction temperature sensor
• Reads thermocouple
• Supports automatic or one-shot conversion modes
• Supports built-in cold-junction offset compensation
• Supports 50/60Hz mains power frequency noise rejection
• Supports setting temperature interrupt thresholds
• Supports setting/checking for all fault types supported by the sensor
• Supports setting thermocouple type

Requirements

P1/SPIN1:

• spin-standard-library
• 1 extra core/cog for the PASM SPI engine (none if bytecode-based engine is used)

P2/SPIN2:

• p2-spin-standard-library

Compiler Compatibility

Processor	Language	Compiler	Backend	Status
P1	SPIN1	FlexSpin (6.2.1)	Bytecode	OK
P1	SPIN1	FlexSpin (6.2.1)	Native/PASM	OK
P2	SPIN2	FlexSpin (6.2.1)	NuCode	FTBFS
P2	SPIN2	FlexSpin (6.2.1)	Native/PASM2	OK

(other versions or toolchains not listed are not supported, and may or may not work)

Limitations

• The chip has no known identification register, so the driver will start successfully as long as the SPI engine does

max31856-spin's Issues

Temps above approx 63C are negated

Rising above approx. 63 deg Celsius, temperatures are reported negative. True negative temps are still reported correctly.

P1: Driver malfunctions when using bytecode-based SPI engine

The temperature data doesn't update when the operating mode is set to continuous, and if the binary is continuously re-loaded, the data does change, but is incorrect. The thermocouple type read back is also incorrect. Experimenting with different SPI modes seems to affect the behavior, but doesn't restore correct functionality.

Rewrite ColdJuncOffset() param

It should take degrees as a parameter, rather than a reg value.

Sign isn't handled correctly

The sign bit isn't extended to bit 31 in ColdJuncTemp() or ThermocoupleTemp(), so negative temperatures aren't reported correctly.